Puncture-type tester for airplane fabrics



March 1l, `i952 T. HUGHES PUNCTURE-TYPE TESTER FOR AIRPLANE FABRICS Filed Feb. 2l

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WN \N NN Patented Mar. 11, 1952 PUNCTURE-TYPE` TESTER FOR AIRPLANE FABRICS Thomas E. Hughes, Mobile, Alla., assigner of one-half: to W. A. Wood Application February 21, 1950, Serial No. 1.45.511-

(Granted under the act of March 3, 1883,A as` 8.b ClaimA s.

amended. April 30, 1928; 370. 0. G. 757) The invention described herein may bef Ina-mie factured and used by or for the Goverment for governmental purposes withoutpayment to me of any royalty thereon.

This invention relates to a readily portable tester of the puncture type for airplane fabrics 4and other sheet materials. In i-t4 a puncture point may be adjustably spring loaded soA aste limit the pressure which can be pu-ton` thepoint.

One of the objects of the invention is to` provide a device for puncture testing the doped fabric surfaces of aircraft when the fabrics are stretched over wing control surface or other parts of an aircraft. The tester is intended to be used without removing the fabric from the surface over which it is stretched.

Another object is to make a tester of the above character in a small, light form, approximately the size of a two cell pen-type flashlight and weighing less than one-half pound.

Another object is to make af fabric tester which will give reproducible results and will not be deleteriously influenced by the presence of many -coats of dope on the fabric and which, if it punctures a fabric at all, will make only a smalllpuncture which may be readily sealed.

Another object is to make a tester of the above character in which the amount of force* to be applied to the fabric to accomplish a puncture can be regulated so that no puncture will take place if the fabric is in satisfactory condition.

Another object is to provide a fabric tester which will stretch a fabric uniformly toA apredetermined degree in all radial directions before a puncture is attempted.

Other objects will be apparent from the hereafter described details to a person skilled in the art.

Referring now to the drawings, Fig. l is a side elevation of my tester, shortened by break lines, showing the tension at which the test is to be conducted, set at ten pounds; i

Fig. 2 is a longitudinal section of Fig..1, a` few of the internal parts being shown in partial4 section or unsectioned;

Fig. 3 is a cross section taken on the line 3 3 of Fig. l; l

Fig. 4 is a cross section taken on the line 4--4 of Fig. 1; and

Fig. 5 is a side elevation of a modied puncturing tip, the tip itself being shown unsectioned and the other parts in longitudinal section;

As Will be seen from Fig. l, the instrument is divided into a tip section l0, a barrel section and a dope reservoir I2. I3v is a square ended piece of piano wire which 'accomplishes the actual puncturing of the fabric whenever a puncture takes place.v

In Fig. 21,1 this: point 13 is held within-.a plunger |l'4- by alocking screw |5i which extends transversely through the plunger |4i into a central hole Illy therein which is j-ust slightly larger than the diameter of al piano wire. The outer end ofthe piano Wire tip I3 must be ground off exactly iiat and square and all bur-rsI must be removed so ythat there is a slight, almost imperceptible bevel at the end ot thewwire. This precaution is necessary to prevent any cutting. action which might result from a sharp or jagged edge on the tip i3. Theplun'ger Ik isprovided with` a shouldered portionf I-'I` of greatest diameter which nts snugly in the mainbarrel I8' of the instrument with a sliding t.' A lower shoulder I'9 of the portion I1 'for the position of the tension cup 23.

abuts' a semi-closed end 20 of the barrel I8 through which` the extreme outer end of the plunger I4 projects, also with' a snug slidingV fit. The barrel'V t8 i's externally threaded at its extreme outer end 2li'V to receive athimble 2| which bears a shoulder 2'2 at its outer end.` Surrounding the thimble 2| there` is a tension cup 23`which is also` shouldered at 2'IlV and externally threaded to receive a` positioning sleeve 25v which is internally threaded and` is shouldered at 26 so that aA compression spring 2l may abut it and press' it` outward over the point |3.n A locking ring 28- isl providedtothreadedly engage the exterior surface of' the cup 273` by threads. 30` between theouter end of the sleeve 25 and a rounded outer flange 29 of the cup 23. The function of the ring 28 is to prevent relative motion' between the cup 23 `and the sleeve 25' when the ring is screwed tight against the outer end of the sleeve 25. thus constituting a` longitudinal adjustment The utility of such adjustment resides` in the fact that when the sleeve 25? is moved backward on the cup 23, the. initial compression loading on-` the coil spring 2l is increased, therefore the effort required to move the flange 29` backward to exposethe point Alli is also increased'. Therefore the radial stretching` tension on the fabric inclosed by the flange 29? also increased` and can be regulated.

The plunger I4? extends into the main barrel |81 as a shaft` 3|f` of smaller diameter than the shoulderedlportion I'I. It is preferably hollow and the cavity 32 may contain'a spare point 33 or one oir different diameter from that in use. A screw 34 retains the poi-nt in the cavity; The shaft portion`3| is surrounded by'a compressioncoil spring 35- which abuts2 aA positioning washer 36l which can be seen in elevation in Fig. 4. The washer 36 is backed by a zero-setting sleeve 31 which is threaded both internally and externally. A loadadjusting and indicating plug 38 threadedly engages the sleeve 31 and is milled flat to show a scale 39, preferably graduated` in pounds, which shows the amount of pressure which can be exerted on the point I3. Scale 40 (see Fig. 3) in half units of the scale 39 is milled on the opposite side of the load indicating plug 38.

The extent to which the zero-setting sleeve 31 may project from threaded engagement with the interior of the main barrel I8 is determined by the position of a locking ring 42 which threadedly engages the load-indicating sleeve 31 and abuts the main barrel I8. The locking rings position is adjustable with a Spanner wrench (not shown) which fits a hole 43 in the locking ring 42. A suplemental barrel I8a in which there is an opening 44 extending through both walls, threadedly engages the sleeve 31 as far as the locking ring 42. The scales 39 or 40 may be observed through the opening 44. A iiducial mark 4| may be provided on the` zero-settingsleeve 31.

For the purpose of thumb adjustment, the load-adjusting and -indicating plug 38 is provided with a knurled head 45.. VIn order to give an indication of changes in loading due to hand rotation of the plug 38, aclick device has been provided. As can be seenV from Fig. 4, the washer 36 is provided with a ridge 46 which ts a trough (not shown) at the Ybase of the plug. When the trough is aligned with the ridge, a click is heard or felt as the washer 36 snaps against the base of the plug. This click is repeated every half revolution of the plug, and ordinarily indicates increase or decrease of one-half pound in point loading. A small detent 36a (Fig. 3) is provided to prevent the washer 36 from turning with the plug. The detent 36a fits an internal longitudinal channel in the sleeve 31 (Fig. 4).

Referring now to Fig. 5 the plunger I4' is conical and bears the point I3' after the manner of a sharpened lead pencil. This form of point is useful for modified tests.

A feature which has been found extremely useful and convenient is a dope reservoir 41 and applicator 48 combined with a closure 49. When the reservoir contains airplane dope, the hole resulting from a puncture by the point I3 can immediately be lled by applying dope with the applicator, so there is no substantial damage due to testing with this device. It may be omitted if not desired.

USE FOR TESTING Calibration Zero-setting is performed by changing the longitudinal position of the calibration-indicating sleeve 31. To do so, the barrel Section I6a is first removed from the sleeve 31, the locking ring 43 is loosened and rotated toward the outer end of the sleeve 31. If it is desired to increase the compression on the spring 35, the sleeve 31 is screwed further into the barrel section 8 and vice-versa. Exact values can be obtained by pressing upward on the point I3 with a scale beam of a weighing scale (not shown) which beam has a heel portion extending beyond the fulcrum point. The tester is held in a vise for this purpose. While the tester is in such position, the ring 43 being locked against barrel portion I8, the load indicating plug 38 is screwed out until the same number of pounds is indicated on the weighing scale beam and on the scale 39 opposite 4 the duclal mark 4I. It is to be noted that the sleeve 31 cannot be moved so far into the barrel portion I8 so that the spring 35 could become wholly compressed, i. e. that its coils would abut each other. The short length that the plunger I4 projects beyond shoulder 20 and the short length of the point I3 also contribute to this result. Consequently the pressure that can be put on the point I3 in ordinary use is limited, no i matter what calibration setting is used. The utility of the zero-setting feature of the invention is that a range of settings can be provided for each kind of fabric under consideration, or the tester can even be set to a proper range for paper, corrugated boxboard or the like.

The preferred diameter of the Wire tip I3 is .051" and it should have a sharply squared end. The spring loading of the inner compression coil spring 35 is preferred to range from '1 to 12 pounds for airplane doped fabrics. Recalibration, as below described. should be performed when a different spring 35 is employed. The tension cup 23 is loaded preferably to a 10 pound pressure by the compression spring 21 for such use, the pressure on this spring being such that it will be fully compressed before the point I3 can exert any pressure on the manipulation fabric.

The tip section I0 of the tester is held perpendicular to the surface of the fabric to be tested, the operators hand grasping the tester lby its hand section II. The thumb may be applied over the closure 49. Pressure is applied. the loading of compression coil spring 35 being adjusted by turning the load indicating plug 38 to minimum value as indicated on its scale, until the tip I3 contacts and presses upon the surface being tested, as fully as the spring loading will permit. This operation causes the rounded flange 29 of the thimble 25 to press upon the fabric surface or doped surface as the case may be and stretch it radially in all directions in a plane at right angles to the vertical axis of the instrument to as full an extent as the compressive strength of the spring 21 Will allow. After the spring 21 is fully compressed, then the point I3 yields retracting the plunger I4 and compressing spring 35 until a, pressure is reached at which the point I3 will puncture the stretched fabric provided that the fabric can be punctured -within the compression range of spring 35. If the fabric is doped, a plug is rst punched out of the dope coating and this plug acts as the actual puncturing point. This is an advantage since nol cutting of the fabric, only shearing, takes place under such circumstances. Pressure is maintained for two or three seconds. If the point I3 does not puncture the fabric, the spring loading is increased by 0.5 or l pound increments, as desired, and the test repeated. The procedure is continued until a setting is reached which results in the point I3 puncturing the fabric in a majority of the trials. The reading on the adjustment for the spring loading is considered as a measure of the strength of the fabric. The instrument can also be used with the adjustment set at a specific predetermined value and if no penetration of the fabric occurs when it is tested, its condition is then considered to be satisfactory.

What I claim is:

1. A tester for ascertaining the puncture strength of stretched fabrics and the like which comprises a puncturing point, a tubular barrel means including a plunger bearing said pointrat the outer end thereof and a surrounding coil spring in said barrel for initially spring loading said point, means adj ustably mounted in said barrel for varying the point at which said coil spring is based whereby to lengthen or shorten said spring, fabric-stretching means surrounding said puncture point and means including a springpressed positioning sleeve threadedly engaging said fabric-stretching means for creating and adjustably setting a spring pressure on said stretching means whereby to position said means ahead of the puncture point until pressure sufcient to overcome the resistance of the stretching means spring pressure is applied to the extreme outer end of the fabric stretching means.

2. A tester for ascertaining the puncture strength of stretched fabrics which comprises a main barrel portion, an auxiliary barrel portion, a locking ring separating the two portions, a threaded positioning sleeve upon which both barrel portions and said locking ring are threadedly engaged, a plunger centrally carried within said main barrel portion, a compression coil spring .surrounding said plunger, compression-regulating means adjustably positioned in said positioning sleeve the outer end of said means being visible within the auxiliary barrel portion, a puncture point comprising a short length of wire positioned in the outer end of said plunger and a fabric-stretching means including a tension cup and a coil spring surrounding the barrel auxiliary portion, said spring biasing said tension cup, said fabric-means being thereby yieldably positioned to surround said main barrel portion and said puncture point.

3. A tester for ascertaining the puncture strength of stretched fabrics which comprises a main barrel portion, an auxiliary barrel portion, a locking ring separating the two barrel portions, a threaded positioning sleeve upon which both barrel portions and said locking ring are threadedly engaged, a plunger centrally carried within said main barrel portion, a compression coil spring surrounding said plunger, compression-regulating means adjustably positioned in said positioning sleeve withthe outer end of said means being visible within the auxiliary barrel portion, the outer end of said plunger terminating in a fabric puncture point, a fabric-stretching thimble surrounding said main barrel adjacent to the outer end of said plunger in sliding relation with respect to said barrel, and spring means to yieldably resist sliding movement of said thimble inwardly along said main barrel.

4. A tester for ascertaining the puncture strength of stretched fabric which comprises a main barrel portion of different internal diameters, internal threads on the larger diameter portion, an internally threaded auxiliary barrel portion, a zero-setting sleeve threadedly engaging the two portions, internal and external threads on said sleeve, a locking ring engaging the external threads on the sleeve between the two barternal shoulder at the outer end of said main barrel portion against which said plunger is arranged to abut, a larger diameter portion on said plunger toward its outer end, said larger diameter portion being arranged to abut said internal shoulder and to slidably t, the barrel portion of lesser internal diameter, a compression coil spring encircling said plunger and abutting its larger diameter portion and said washer at opposite ends thereof and point-holding means in the extreme outer end of said plunger.

5. A tester according to claim 4 and in addition a point consisting of a short length of music wire, the outer end of which has been squared, removably positioned in said point-holding means.

6. A tester according to claim 5 and in addition an outer coil spring positioned about the main barrel at the lesser diameter thereof, a shoulder on the outer surface of said main barrel adjacent substantially the points of change of internal diameter against which shoulder the inner end of said spring abuts, a fabric stretching thimble slidably positioned on the outer end of said main barrel portion whereby normally to protect the point, threads on the outer surface of said thimble and a positioning sleeve threadedly engaging the outer surface of said thimble and an inner shoulder on said positioning sleeve against which the outer end of said outer coil spring is arranged to abut, whereby the force necessary to push the thimble and sleeve back on the main barrel portion may be regulated by adjusting the threaded position of the outer sleeve on the thimble.

7. In combination in a fabric tester of the puncture type, a puncture point, a plunger in which said puncture point is held, means for adjustably spring loading said puncture point, a barrel substantially surrounding said plunger and said spring loading means, a tension cup substantially surrounding the outer end of said barrel, said plunger and said plunger point and extending beyond the outer end of said point, spring means surrounding said barrel for adjustably loading said tension cup against pressure on the outer rim thereof and means for locking said adjustable loading means including a positioning sleeve threadedly engaging said tension cup and biased by said spring means.

8. In the combination set forth in claim 7 having such a relation between the means for adjustably loading the puncture point and the spring means surrounding the barrel that the barrelsurrounding spring is materially weaker toward compression and the means for spring loading the puncture point.

THOMAS E. HUGHES.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,452,944 Webb Apr. 24, 1923 2,522,544 Seyboth Sept. 19, 1950 FOREIGN PATENTS Number Country Date 687,819 France May 5, 1930 

